1. Field of Invention
The present invention relates to a semiconductor process. More particularly, the present invention relates to photoresist coating process.
2. Description of Related Art
Generally speaking, a fabrication process of a semiconductor device, which includes thin film deposition, photolithograph, etching, ion implantation and thermal process, etc., is complicated, and the photolithography process is the most essential step in the entire semiconductor process. A photolithograph process constitutes mainly with the three steps of photoresist coating, exposure and development.
The conventional photoresisting coating process includes three major parts. Firstly, a wafer is placed on a platform of a spinner and is then rotated at high speed to remove the dust from the surface of the wafer. Thereafter, a photoresist material is provided to the surface of the wafer, and by controlling the rotational speed of the wafer, the photoresist material is evenly coated on the wafer to form a photoresist layer. After this, the supply of the photoresist material layer is terminated and the thickness of the photoresist layer is adjusted by controlling the rotational speed of the wafer.
The even coating of the photoresist material for fully covering the wafer strongly influences the accuracy of the pattern transfer. However, the conventional practice often results with an uneven coating of the photoresist material and an incomplete coverage of the wafer with the photoresist material, or an excessive coating of the photoresist material to fully cover the wafer. As a result, the chances of affecting the accuracy of pattern transfer or the production cost greatly increase. Moreover, the conventional approach often results with a lavish consumption of the photoresist material and high production cost.